Automatic headlight dimming systemtime delay differential bias



Aug. 2l, 1956 R. N. FALGE ETAI. 2,760,114

AUTOMATIC HEADLIGHT DIMMIMG SYSTEM TIME DELAY DIFFERENTIAL BIAS Attorneys Aug 21, l956 R. N. FALGE Erm.

AUTOMATIC HEADLIGHT DIMMING SYSTEM TIME DELAY DIFFERENTIAL BIAS 2 Sheets-Sheet 2 Filed Jan. 21, 1953 United States Patent O AUTOMATIC HEADLIGHT DIMNIING SYSTEM- TIME DELAY DIFFERENTIAL BIAS Robert N. Falge, Charles W. Miller, and George W. Onksen, Anderson, Ind., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application January 21, 1953, Serial No. 332,368

10 Claims. (Cl. 315-83) This invention relates to light actuated control systems and more particularly to light actuated headlamp dimming control systems for automotive vehicles. Automatic headlamp dimming systems which are controlled by the oncoming lights from an approaching vehicle have recently been placed on the market. These systems mainH tain the headl inps of the automobile on high or long range driving beams when no cars are approaching from the opposite direction but automatically switch to low or short range beams when a car approaches from the opposite direction and reaches a predetermined distance. As the approaching car passes and the impinging light is removed from the photosensitive member, the switching means automatically returns to high beam or long range energization.

These devices are quite sensitive and will switch from high beam to low `beam when an approaching car is, for example, a quarter of a mile away. As soon as the operated cars headlarnps switch to low beam the approaching driver usually switches his lights to low beam in courtesy. When this occurs the amount of illumination falling upon the photocell or photosensitive control is immediately considerably reduced and would permit the automatic system to return to high beam energization unless some provisions were made to prevent this action. In some devices this is overcome by changing the sensitivity of the system upon switching from high beam to low beam actuation. Thus if the control system is made, for example, many times as sensitive when it is switched from high beam to low beam control, it will require much less light on the photosensitive means to retain it in low beam position than it would to switch the system to that position. Of course, it is only necessary to maintain this increased sensitivity until the approaching vehicle has arrived at a point at which the illumination falling on the photocell has increased to the original Vahle. Also, as soon as the cars have passed, it is desired to return to high beam illumination as soon as possible.

lf the increased sensitivity is maintained throughout the entire period of low beam energization, upon the passage of the two cars a small amount of extraneous light from any other source whatsoever may tend to hold the filaments on low beam energization rather than return them quickly to high beam. For example, additional cars at too great a distance to originally cause the system to switch to low beam may cause it to stay on low beam once it has been switched to that position. In some instances street lights which would not ordinarily cause the original switching actuation will maintain the device in low beam position once it has been switched, and, lastly, during the twilight period when the sky is not entirely dark but headlights are necessary there is sometimes a sufficient amount of rcilected sky light to hold the beams on low once they have been switched to that position.

it would, therefore, be advantageous to return the systern to a lower sensitivity at some intermediate time prior to the time when the actuating source of light is removed, such as by passage of the cars, so that when "ice the two cars do pass, the system will be in condition for rapid return to high beam illumination and extraneous lights or too distant sources of light will not cause the system to hold on low beam.

It is, therefore, an object in making this invention to provide means for changing the sensitivity of an automatic headlamp dimming system at some predetermined intermediate time after its switching actuation.

lt is a further object in making this invention to provide a light sensitive system in which the sensitivity thereof is changed upon actuation, and at some later predetermined time is again changed to a third value.

it is a still further object in making this invention to provide a photosensitive control system for the automatic dimming of headlamps having a plurality of sensitivities controlled both by the position of the main switch and a time control means.

lt is a still further object in making this invention to provide a photosensitive headlamp dimming control sys tem which readily returns to high beam energization upon the passage of approaching vehicles.

With the above and other objects in view the invention will be best understood by further reference to the following detailed description and claims and illustrations in the accompanying drawings in which:

Figure l is a schematic circuit diagram of an automatic headlamp dimming control system embodying our invention; and

Figure 2 is a schematic circuit diagram of a modified form of control system also embodying our invention.

Referring now more particularly to the system disclosed in Figure l there is shown therein a main power supply line 2 which is attached to the storage battery or other main source of power in the vehicle. Line 2 extends to tie line i which in turn is connected to a power supply 6 which transforms the low voltage direct current from the battery source to higher voltages that are necessary in the operation of the system. This power supply 6 may take the form of a vibrator-transformer type which are conventional in automotive radio receivers. The ouput from the power supply 6 is applied through line 8 to a potentiometer consisting of a series of resistances it), 12 and 14 in series, the opposite terminal of the resistor 14 being grounded. Resistance 1d has an adjustable tap 16 which is connected through line iii to the photosensitive pickup unit 26 and supplies power thereto which may be ad justed by varying the position of the tap 16.

The output of the photo-sensitive pickup unit 2) is applied through line 22 to one terminal of a resistor 24, the opposite terminal of which is connected through line 26 to one terminal of a potentiometer 3b. The adjustable tap 32 on potentiometer 3d is connected through line 3d to a stationary contact 36 of a relay 38. The remaining terminal of the potentiometer 30 is connected to one terminal of a second potentiometer di), the adjustable tap 4?. of which being directly connected to line 4. T ie line 4d interconnects line 26 and stationary Contact 46 of a second control relay ad. A condenser Sii is connected across lines 22 and 4, and a condenser 52 is connected between line 1i and ground.

A multi-element electronic tube 54 contains two triode sections, the first triode section having a plate S6, a control grid S8 and a cathode 60. The cathode 6d is directly connected to line 4. The control grid 58 is connected to line 22 and its potential is, therefore, determined by the output of the photoelectric unit. Plate S6 is connected to line 62 which in turn is connected to one side of the relay coil 64 of relay 48. The opposite terminal of the relay coil is connected to the power supply through line 66 and obtains actuating power therefrom. Line 62 is also connected to anode 68 of a diode tube 70, the cathode 72 of that tube being connected through line '74 3 with a stationary contact 76 in a manually actuated override switch 78. The movable contact 80 of the switch 78 is directly grounded.

The movable armature 82 of the relay 48 is directly connected to line 4 and is biased by a spring 84 toward the right, as shown in Figure l, to engage a stationary contact 86 when the relay coil is deenergized. The stationary contact 86 is connected to a line 88 which extends to a stationary contact 90 in the conventional foot dimmer switch 92. The relay armature 94 of the relay 38 is likewise spring biased to inoperative position by a spring 96 which would be toward the right as shown in Figure l. In that position the armature 94 engages a stationary contact 98 which is connected through line 100 to a timing condenser 102, the opposite terminal of. which is connected to a tie line 104.

The second triode section of the multi-element electronic tube 54 consists of a cathode 106, a grid 108 and a plate 110. Both cathodes 60 and 106 are directly connected to line 4. The grid 108 of the second triode section is connected to line 104 and also to one terminal of a resistor 112, the opposite terminal of which is connected to line 8S. The plate 110 of the second triode section is connected through line 114 to one terminal of the coil 116 of relay 38. The other terminal of this relay coil is connected to line 66 through tie line 118.

The movable armature 120 of the conventional foot switch 92 is connected through line 122 to one terminal of the coil 124 of a power relay 126. The opposite terminal or' the coil 124 is grounded. The armature 128 of the power relay 126 is biased by a spring 130 to its upper position, as shown in Figure l, in which position it engages a stationary contact 132 and in its lower attracted position when relay coil 124 is energized, the said armature 12S engages a second stationary contact 134. Stationary contact 132 is directly connected to conductive line 136, which extends to the upper beam filaments 35 through conventional connections indicated as Upper. In a similar manner the stationary contact 134 is connected through line 138 to the lower beam laments 137 through conventional connections indicated as "Lower."

ln the operation of this form of our invention, the supply line 2 is connected to a source of power by the closure of any conventional switch on the car and the electronic tubes included in the system are permitted to heat up. lt is to be remembered that the object of this system is to vary the sensitivity for different portions of the operation cycle to provide desired operation. Assuming, for example, that the sensitivity of the amplifying system is unity during the time that the lights are on high beam and no car is approaching, and that it is desired to change the sensitivity to a much higher value upon the initial operation of the system to switch to low beam energization upon the impingement of light rays on the pickup of sufticient intensity for operation. Assume also that it may be desirable to increase the sensitivity ten times. However, with the amplifier ten times as sensitive when the system is switched to low beam, a much smaller amount of light will hold the system on low beam after the immediate approaching car has passed, when it might be desired to return to high beam.

Therefore at some time prior to the instant at which the approaching car passes, it is desirable to change the sensitivity of the system to a relatively lower value, but not return it entirely to the sensitivity which it has when on high beam. As exemplary, it might be returned to a value of three times the sensitivity on high beam. Thus, it is desired to operate on an assumed sensitivity of unity when the high beams are energized and switch to ten times this sensitivity upon initial movement of the switching means to low beam, and then perhaps change to three times the initial sensitivity prior to return to high beam.

In the operation of the system shown in Figure l, relay 48 is the sensitive relay whose position controls the energization of the high r low beams through. of course, the

ill)

power relay 126. When relay 4S is energized to hold its armature 82 against stationary contact 46, then no circuit is completed to the operating coil 124 of the power relay 126 and spring 130, therefore, holds armature 128 in its uppermost position, closing switch 12S-132, and completing an obvious circuit to the upper beam filaments. On the other hand, when relay 48 is deenergized so that spring 84 pulls the armature 82 to the right, as shown in Figure l, and closes switch `82--86, then a circuit is completed to relay coil 124 as follows: power line f5, linc 4, armature 82, contact 86, line S8, contact 90, movable switch arm 120, line 122, relay coil 124 to ground. Thus, energization of relay coil 124 attracts armature 128, pulling it to its lower position, as shown in Figure l, and completing an obvious circuit to the low beam filaments, and at the same time breaking the circuit to the upper beam filaments.

The energization of the relay 48 is in turn controlled by current flow through the first triode section of amplitying tube 54. It will be obvious that the operating coil 64 of the sensitive relay 48 is in series with the first triode section of tube 54, and when sutiicient current is conducted through this section, the relay will attract its armature, but when the current fiow through this section is insuicient, the spring 84 will overcome the attraction of the coil 64 and the armature will move to the righthand position. The conductivity of this triode section is, of course, controlled by the control grid 58, the potential of which is in turn determined by the output of the photo pickup unit 20. When no light falls on the pickup 20, the potential of grid 58 is determined to be sufficiently high to permit conductivity of this triode and, therefore, energization of coil 64, so that it holds its armature 82 in the left-hand position, which in turn determines that the upper beam filaments shall be energized.

When light does fall on the photocell, which increases the current iiow through line 22 and resistor 24, then the potential of the grid 58 is reduced, and if the increase in light intensity is suliicient, will cause the grid S8 to fall to a point where it reduces the iiow of current through the tube and spring 84 will pull armature 32 away to non-energized position, thus switching the lights to lov/ beam. When this occurs, a short circuit path around potentiometers 30 and 40 is opened, and they are immediately inserted into the grid circuit, automatically increasing the sensitivity of the amplifier to a degree depending upon the values of these resistors. This results in changing the potential of the grid to a much lower value for tube control with the same amount of light impinging on the photocell pickup. In the suggested example, the amplifier may be ten times as sensitive at this point as it was without the resistors 30 and 40 in circuit. The radiation from the headlamps of the car proceeding in the opposite direction is now able to hold the system on lower beam operation even though the approaching driver dims his headlamps.

During the time that the system was on high beam operation, relay coil 116 of the auxiliary relay 38 was deenergized due to the fact that the second triode section of the tube 54 was biased to cutoff, as will be described, and since the coil 116 was deenergized, the biasing spring 96 of this relay held the armature 94 to right to engage stationary contact 98. This connects the condenser 102 to the power line 4, and it is charged by the power source during this portion of the cycle of operation which applies a negative ybias to the grid 108 and maintains this portion of the tube nonconductive so that relay coil 116 is not energized. When light impinges on the photoelectric pickup unit 20, causing grid 58 to be driven negative and cutting off conductance through the first triode section 0E the tube 54 to deenergize the relay coil 64 and switch to low beam filaments, resistor 112 is connected in parallel to condenser 102 through an obvious circuit. Condenser 182 will, therefore, bleed oft through resistor 112, allowing the grid 108 to approach the potential of the cathode 106 in a predetermined time interval, depending upon the values of capacitance and resistance used.

When the condenser 102 has discharged and the potential on grid 108 has approached that on cathode 106, this second triode section will conduct, energizing relay coil 116. This energization attracts armature 94, closing the switch 94-36 to short out an additional portion of the resistances 30 and 40, depending upon the setting of their adjustable taps. This reduces the sensitivity of the 1first amplifier section by changing the potential on grid 58 again and returns the sensitivity to a lower value than that to which it was originally switched, but not to its initial sensitivity due to the fact that a certain portion of resistance 30 is still included in the grid circuit. As an example, this might cause the return to three times the initial sensitivity from a value of ten times that sensitivity. When the approaching car passes the vehicle being operated, therefore, it will be necessary to have considerably more light impinging on the photocell pickup than was necessary to hold it down shortly after switching to low beam, and the system would be much more apt to return to high beam than if it retained the much higher sensitivity (i. e., :1) which it utilized upon initial switching to low beam. lr" insufficient light is now available due to no more approaching cars or other sources of light, upon passage of the approaching vehicle, the lights will return to high beam due to conductance through the first tricde section of tube 54 and energization of relay coil The time period, following initial switching to low in which it is desired to have the system change sensitivity to a lower Value, can be determined by the values of the condenser-resistance circuit 102-112.

1t, after the system automatically switches to low beam, it is desired to flash the oncoming driver, in the event that he may have retained high beam illumination, this may be accomplished by closure of the overriding switch '73 which completes a bypass circuit to ground around the first triode section of the tube 54 through diode 70. Whenever switch i6-80 is closed, relay coil 64 is energlzed from the power source through the diode 70 to ground, and thus armature 82 will be drawn to its lefthand position to provide upper beam illumination.

Figure 2 discloses a modified form of our invention which operates in substantially the same manner; that is, it provides for a switching of sensitivity from a unit vaine to a much higher value upon initial switching to low beam energization, and then a return to a lower value of sensitivity after a predetermined time interval prior Yto the removal of the light source entirely causing a return to high beam energization. In this circuit there is similarly provided a main power supply line 140 which may extend to the conventional lighting switch of a vehicle, which line is connected to a tie line 142 interconnecting the power supply 144 and the movable armature 146 of the sensitive relay 148. This armature is biased away from the energizing coil by spring 150, whose force may be overcome by the relay coil 152. The power supply 144 is of the vibrator type, although any other suitable means may be used to change low voltage direct current to a higher voltage for supplying various portions of the system. Relay coil 152 is connected through line 154 to the power supply and has its other terminal connected through line 156 to both anodes 158 and 160 of the two triode sections of the `amplifying tube 162.

The relay armature 146 oscillates between two fixed contacts 164 and 166, engaging contact 164 when the relay coil 152 is energized and 166 when deenergized. Stationary contact 164 is connected through line 168 to an intermediate point between resistance 170 and variable resistance 172 and also through condenser 174 to supply line 142. Stationary contact 166 of the relay 148 is connected through line 176 with stationary contact 178 of the conventional foot switch 180.

A high voltage line 1182 extending from the power supply 144 is connected to one terminal of a tapped re- 6 sistance 184, the opposite terminal of which is connected through two series resistors 186 and 188 to ground. This provides the high Voltage supply for the photosensitive pickup unit 190, which is connected thereto through tap 192 on resistor 184 and conductive line 194. The output ot' the photoelectric pickup unit is connected to line 196 which extends to one terminal of the resistor 170, previously mentioned, and also to the control grid 198 of the first triode section of tube 162. Cathode 200 of the first section of the tube is directly connected to supply line 142 which likewise feeds the filaments of the tube 162. The grid 202 and cathode 204 of the second triode section of the tube 162 are 'connected together and to line 206, which extends to stationary contact 208 in an overriding switch 216, the movable contact 212 of which is directly connected to ground.

The variable tap 214 on resistor 172 is connected through the line 216 to a conductive bi-metal strip 218 which is adapted to change its configuration upon the application of heat thereto and which carries a switch contact point 220. Mounted in spaced relation to contact 220 is a stationary contact 222 which is connect-ed through line 224 to supply line 142. A second tapped resistor 226 is connected in series with tapped resistor 172 and the adjustable tap 228 on the resistor 226 is connected to supply line 142. A second spaced stationary contact 230 of the conventional foo-t switch 180 is connected through line 232 to a movable `armature 234 of power relay 236 and also to supply line 140. The armature 234 of the power rel-ay 236 is biased by `a spring 238 and oscillates between two fixed contacts 240 and 242. Stationary contact 240 is connected directly to line 244 which extends to the conventional upper beam filaments 241 through connection labelled Upper and stationary contact 242 is connected through line 246 to the conventional lower headlight filaments 243 through connection labelled Lower :and lalso to a heating coil 250 mounted in proximity to the bi-metal member 218 to provide heat for the same. The opposite end of the heating coil 259 is grounded. The movable switch arm 252 of the conventional foot switch 180 is connected through line 254 to the relay coil 256 of the power relay 236, and the opposite terminal of the relay coil is grounded. In this form of our invention the sensitivity of the amplifier is controlled by two difierent switching means, the first being the armature 146 of the sensitive control relay 148 which removes a short circuit `around resistances 226 and 172 and .places them in the grid circuit ofthe amplifier upon initial switching to low beam; and the second being the thermal time delay switch 228-222 which removes a predetermined portion of the inserted resistance in the grid circuit of the amplifier at a predetermined time after the original switching.

The operation of this system specifically is as follows: supply line is energized by the closure of some switch means in the Vehicle, and if there is no light or insufficient light falling on the photosensitive pickup unit 198, relay coil 152 is energized through conductive flow through the first triode section of the tube 162. The potential on the control grid 198 is determined by the resistance in series with the output of the photopickup unit 190, Upon the approach of a vehicle from the opposite direction and the impingement of light upon the photo pickup unit 190, current flow through line 196 and resistance 170 reduces the potential on the grid 198 to such a point that the conductance through the first triode section is 4cut down and the relay coil 152 releases its armature 146 to the force of the biasing spring 150. The movement of the armature 146 away from stationary contact 164 breaks the shunting circuit around resistors 172 and 226 and inserts them in the grid circuit which increases the sensitivity of the system, making a smaller amount of light falling on the photocell or smaller output from the photocell unit sufi'icient to maintain tube cutoff and low beam energization.

It will be noted, however, that as soon as the power relay 236 is energized bythe movement of the armature M6 to its right-hand position in contact with stationary contact i166 and the resultant switching of armature 234 of the said power relay to low beam position, a circuit is completed to the heating coil 250 from the power line 14() so that as soon as the lights are switched to low beam, heat is applied to the bi-metal strip 218 and it begins to warp in direction to close contacts 220 and 222 and after a. predetermined Set interval these contacts will close. When they do so, they short out or shunt that portion the two resistances i172 and 226 between the adjustable taps .2i/i and 228, thus returning the sensitivity of the system to some figure between the original high beam sensitivity and that initially obtained when the system switched to low beam operation.

Thus as in the previous instance, there are obtained three levels of sensitivity: one when the system is on high beam, which is the least sensitive of the three conditions;

second, when the system is initially switched to low beam operation, which is the highest condition of sensitivity; and third, an intermediate sensitivity which is obtained at a predetermined time interval after initial switching to low beam energization, but prior to the return to high beam condition. The exact values of these sensitivities and their interrelationship can be adjusted by selection of the values of resistances used and by moving the taps 214 and 228 respectively along resistances 172 and 226.

We claim:

l. A control system including multiple filament headlamps, a source of electrical power, switching means for alternately energizing different headlamp filaments connected to the source and to the filaments, light sensitive means connected to the source of power having an output circuit, resistance means in series in the output circuit of the light sensitive means, a plurality of shunting means connected across different portions of the resistance means, further switching means in each shunting circuit, control means connected to said output circuit and to the source of electrical power, independent actuating means for each further switching means connected to the control means to be operated thereby, and time delay means incorporated with one of the actuating means to cause it to operate at a predetermined interval following the operation of the other of said actuating means.

2. A control circuit including multiple filament headlamps, a source of electrical power, switching means connected to said source and to said filaments for alternately energizing the same, light sensitive means connected to the source of power and having an output circuit, resistance means connected in said output circuit across which control voltages are developed by changes in current fiow therethrough incurred by changes in illumination falling on said light sensitive means, an electron tube having a grid and plate, said grid being connected to said light sensitive output circuit for controlling the flow of current through said electron tube, dependent upon the voltage of said output circuit, control means connected in the plate circuit of the electron tube and to the switching means for controlling the energization of the headlight filaments, a plurality of adjustable taps on said resistance means, a shunt circuit conne ted to said adjustable taps, further switching means in said shunt circuit, and time delay means for actuating said last-named switching means to cause the shunting out of a portion of the resistance during a predetermined part of the cycle of operation of the system.

3. A control system including multi-filament lamps, a source of electrical power, switching means connected to the filaments and to the source of power for alternately energizing the sante, a light sensitive unit connected to the source of power and having an output circuit, ampliner means connected to the output circuit of the said light sensitive means, means for determining the sensitivity of the amplifier means including resistance means in the output circuit of the light sensitive means, and means for applying a multiplicity of differing sensitivities to said amplifier including a plurality of shunting means connected across differing portions of the resistance means, and independent switching means connected in each shunting means for controlling the shunting means during differing portions of the operating cycle.

4. A control system, a circuit controlling device, a source of electrical power, light sensitive means connected to said source of power and having an output circuit, amplifying means connected to the output circuit of the light sensitive means and to the circuit controlling device so that the output of the light sensitive means will control the energization of the circuit controlling device, means for changing the sensitivity of the amplifying means to a plurality of different values connected to the amplifying means, and multiple switching means connected to the sensitivity changing means to be actuated in sequence for varying the sensitivity of the amplifier.

5. A control system, a circuit controlling device, a source of electrical power, light sensitive means connected to said source of power and having an output circuit, amplifying means connected to the output circuit of the light sensitive means and to the circuit controlling device so that the output of the light sensitive means will control the energization of the circuit controlling device, means for changing the sensitivity of the amplifying means to a plurality of different values, a first switching means connected to the sensitivity changing means and controlled by the circuit controlling device to vary a portion of the sensitivity changing means, and a second delayed switching means connected to a different portion of the sensitivity changing means to further vary the same a predetermined time period after the first.

6. In an electric circuit, a light sensitive unit, a source of electrical power connected to said unit, means connected to said light sensitive unit to amplify the output thereof and means connected to said last-named means to vary the amplification of the output of said light sensitive unit in a plurality of predetermined fixed steps.

7. A control system for automatically energizing alternate circuits, a source of electrical power, switching means for alternately energizing said different circuits connected to the source and to the circuits, light sensitive means connected to the source of power having an output circuit, resistance means in the output circuit of the light sensitive means across which voltages are developed, a plurality of shunting circuits connected across different portions of the resistance means, further switching means in each shunting circuit, a plurality of independent means connected to the source of power and the output circuit of the light sensitive means, whose energization is controlled by the light sensitive means for sequentially actuating each further switching means in timed relation to provide different amounts of effective resistance in thc output circuit at different portions of the operating cycle, and actuating means for the first-named switching means connected to one of the further switching means and controlled thereby.

8. A control system including multi-beam lights, a source of electric power, a light sensitive unit connected to said source of power, an output circuit for said light sensitive means including resistance means, an electron amplifier tube having a grid and plate circuit, said grid circuit being connected to said resistance means, a control relay coil connected in the plate circuit of said electron tube, a shunt circuit connected across a portion of the resistor means, switching means in said shunt circuit, a second switching means connected to the multi-beam lamps for controlling the beam energization, both of said switching means being controlled by said relay coil means, a second shunt circuit connected across a different portion of the resistance means, third switching means in said second shunt circuit, second relay coil means for actuating said third switching means, and control means for the last-named relay coil means including an electron discharge tube, biasing means for said last-named tube connected thereto and time delay means connected to the biasing means and to the second switching means to prevent conduction through said tube to energize said second-named relay coil for a predetermined time after the actuation of said iirst relay coil by the light sensitive unit.

9. A control system including multi-beam lights, a source of electric power, a light sensitive unit connected to said source, an output circuit for said light sensitive means including resistance means, an electron amplifier tube having a grid and plate circuit, said grid circuit being connected to said resistance means, a control relay coil connected in the plate circuit of said electron tube, a shunt circuit connected across a portion of the resistance means, switching means in said shunt circuit, a second switching means connected to the multi-beam lights for controlling the beam energization, both of said switching means being controlled by said relay coil means, a second shunt circuit connected across a differing portion of the resistance means, third switching means in said Second shunt circuit, second relay coil means for actuating said third switching means in said second shunt circuit, a second electron discharge tube having a plate and grid, said plate being connected to `said second relay coil means to control the energization thereof, a condenser means connected to said grid and to the switching means actuated by the second relay coil to bias said grid and control the current ow through the second-named electron tube, and resistance means connected to said condenser and source of power so that said condenser may charge during portions of theV control cycle to bias said second-named electron tube to cutol, but discharge during a predetermined time interval 10 and provide conduction through said second-named tube to cause energizaton of said second relay coil during a different portion of the control cycle.

10. A control system including multi-beam lights, a

'source of electric power, a light sensitive unit connected to said source, an output circuit for said light sensitive means including resistance means, an electron amplifier tube having a grid and plate circuit, said grid circuit being connected to said resistance means, a control relay coil connected in the plate circuit of said electron tube, a shunt circuit connected across a portion of the resistance means, switching means in said shunt circuit, a second switching means connected to the muiti-beam lights for controlling the beam energization, both of said switching means being controlled by said relay coil means, a second shunt circuit connected across a differing portion of the resistance means, a third switching means in said second shunt circuit, lai-metallic time delay means for actuating said third switching means, and heating means for the lai-metallic time delay means connected to said second switching means so that it is energized when the lights are initially switched to a different beam, but closure of the second shunting circuit is delayed during the period of warpage of the bi-metallic element.

References Cited in the tile of this patent UNITED STATES PATENTS 

